Our studies of the role of the T4 bacteriophage RNA ligase and polynucleotide kinase has led to the discovery of two new E. coli genes lit and prr which map at 25 and 29 minutes, respectively. The products of these genes interact with cis-acting sites on bacteriophage DNAs to prevent the expression of the entire bacteriophage genome. The DNA sites are sometimes modified, probably covalently, in a way which affects their utilization. We propose to clone the lit and prr genes and determine their products. We shall also continue our characterization of the sites. The gol site of T4 has already been mapped and five mutations in the site located by DNA sequencing. We shall sequence more mutations in the site located by DNA sequencing. We shall sequence more mutations in the site including some which inactivate gp23 encoded by the same stretch of DNA and any others which are lethal to the phage. In addition, we shall determine the modification which occurs at the site and whether RNAs are made on the site which affect its utilization. We whall also map the sites on Lambda DNA affected by the prr locus and determine the modification of DNA promoted by the prr locus and the unf/alc region of T4.